Hereinafter, an idle mode and a sleep mode will be briefly described.
If a user equipment (UE) is turned on, the UE automatically or manually selects a public land mobile network (PLMN) to be accessed, and receives cell control information which is suitable for receiving a service in the selected PLMN. This control information may include system information and a cell broadcast message transmitted from a cell.
The UE may acquire downlink scrambling code and frame synchronization information from the control information. Although the UE is in a state in which this control information can be received from the cell, the UE may be still in the idle mode. That is, the idle mode of the UE indicates a state in which the UE does not establish radio resource control (RRC) connection with a UMTS Terrestrial Radio Access Network (UTRAN) and the location information of the UE cannot be checked in the network.
Accordingly, the UE in the idle mode can be distinguished using an international mobile subscribe identity (IMSI), a temporary mobile subscribe identity (TMSI) or a packet-TMSI (P-TMSI) which is the identity of the UE used on a network access system (NAS). If the UE transmits an RRC connection request message to the UTRAN and activates the RRC connection, the UE transitions to a connection mode.
FIG. 1 is a view showing an example of a paging subframe structure and a paging discontinuous reception (DRX) cycle of a UE in an idle mode.
FIG. 1 shows the paging DRX cycle which can be used by the UE in the idle mode or the sleep mode. The idle mode or the sleep mode of the UE indicates a state in which the UE does not exchange data with a system. In this case, the UE can check whether or not there is a call directed to the UE using the paging DRX cycle.
Generally, one paging DRX cycle may be configured by n paging occasions and each of the paging occasions may be configured by m subframes. One of the subframes in the paging occasion may be used as a paging subframe, and UEs which select the same paging occasion may awake once on at the same subframe in the paging DRX cycle (or the paging occasion) so as to check whether or not there is a call directed to the UE by a paging indicator-radio network temporary identifier (PI-RNTI).
FIG. 1 schematically shows the structure of the paging subframe. The subframe which is selected as the paging subframe may be configured by a paging indicator channel (PICH) and a paging channel (PCH) for transmitting a paging message. The PICH indicates the location of the PCH, via which the actual paging message is transmitted, as a control channel for paging. In the drawings showing the embodiments of the present invention, the PICH is represented by a PI.
Generally, even when broadcasting information is transmitted to the UE in the idle mode or the sleep mode, the PICH and the PCH may be used. The paging subframe structure of FIG. 1 is an example of broadcasting information transmission, which shows the subframe structure in the case where at least one UE is paged within all paging occasions and a paging message and broadcasting information are transmitted together.
FIG. 2 is a view showing an example of a process of changing and updating system information.
FIG. 2 shows a method of changing system information (system units (SUs)) transmitted via a dynamic broadcast channel (DBCH; e.g., a downlink shared channel (DL-SCH)).
If the system information is changed in an (N+1)th broadcast control channel (BCCH) modification period, a base station (BS) notifies the UE of information indicating that the system information is changed in a next modification period, in an nth BCCH modification period. A modification period boundary is defined by SFN mod N (N may be set by the system information).
FIG. 3 is a view showing an example of a method of transmitting a notification message for the change of the system information to UEs in an idle mode or a sleep mode.
DBCH update notification information is transmitted via the PCH, via which the paging message is transmitted, such that all UEs can newly receive system information (e.g., SU-n) updated in a next BCCH modification period.
Each of the UEs in the idle mode or the sleep mode performs the following procedure. First, each of the UEs receives a master information block (MIB) via a primary broadcast channel (PBCH) and receives a system unit including system information via a DBCH.
Each of the UEs may select a paging occasion of each UE using a parameter received via the system information. The UE may check whether or not a PICH has transmitted using a PI-RNTI in a paging occasion of a paging DRX cycle.
If the system information transmitted via the DBCH is changed, the BS may transmit the changed system information to the UEs via the PCH. In FIG. 3, if all UEs recognize that the DBCH information is changed in an nth BCCH modification period, the BS transmits the changed system information of the DBCH to the UEs in an (n+1)th BCCH modification period, and the UEs receive the changed system information. Each UE transitions to an active state if there is a paging message directed to the UE and repeatedly performs a paging occasion if there is no paging message directed to the UE.
In FIG. 3, the system information (SI) includes a variety of information such as mobility support and measurement information of the UE in an active state (RRC_connected state) and system information necessary for connecting the UE in the sleep mode or the idle mode (RRC_IDLE state) to the network.
The SI may be generated from a core-network or a BS and managed in an RRC layer. In order to systematically transmit the SI, a system information block (SIB) is configured by combining plural pieces of SI having similar characteristics in the RRC layer. The SI belonging to different SIBs has different characteristics in a transmission repeat cycle as well as contents. Among them, several SIBs are defined by a mater information block (MIB), and the MIB includes reference information or scheduling information of SIBs broadcasted in a cell. The MIB is regularly transmitted via a BCH (mapping to the PBCH of a physical channel), and the UE can readily receive the MIB.
If a UE receives information transmitted by the MIB, the UE no longer requests the update of the information. The SI transmitted by the BS via the PBCH in FIG. 3 is as follows. The SI may include a physical layer parameter, a system frame number, scheduling information of the most frequently repeated scheduling unit (SU-1), and a value tag.
At this time, the physical layer parameter may include a downlink system bandwidth, the number of transmit antennas, and a reference-signal transmit power level.
The BS may transmit an RRC message called a system unit (SU) obtained by combining the SIBs having similar characteristics except SIBs belonging to the MIB. At this time, SU-1 is transmitted in a smallest period (80 ms) and the other SU-n is transmitted in a period which is scheduled in the SU-1.
The BS transmits the SUs to UEs via the DBCH and each of the SUs is configured by a parameter which can be changed. If the system information is changed, all the UEs request the update of the SI. Accordingly, the methods shown in FIGS. 2 and 3 are used for the update of the SI which is generally changed.
FIG. 4 is a view showing an example of a PICH structure which is generally used.
The fields of the PICH which is a control channel of a first layer L1 and a second layer L2 may use the format of a PDCCH used in a downlink (DL) scheduling grant. Such a PICH may be XOR-operated with a CRC using a PI-RNTI instead of a C-RNTI in order to distinguish the PICH from the DL scheduling grant. The UE in the idle mode or the sleep mode blind-decodes the CRC by the PI-RNTI, recognizes that there is a paging message transmitted within a paging occasion, to which the UE belongs, and decodes the PCH.
The fields of the PICH may include DL resource (RB) assignment information, DL MIMO information, a modulation scheme, a payload size, HARQ information and a CRC which is XOR-operated by the PI-RNTI, as shown in FIG. 4.
FIGS. 5 and 6 are views showing one of methods of transmitting broadcasting information to the UEs in the idle mode or the sleep mode.
In order to transmit broadcasting information (e.g., system information change or update) to UEs in the idle mode or the sleep mode, the BS may use a paging DRX cycle. The paging procedure between the UEs and the BS is as follows.
Each of the UEs in the idle mode or the sleep mode may select one paging occasion within a paging DRX cycle by a subframe level. Each of the UEs in the idle mode awakes in a paging subframe corresponding thereto using one paging occasion and checks whether or not paging information has transmitted to each UE.
Referring to FIGS. 5 and 6, a first UE (UE1) selects a first paging occasion within the paging DRX cycle, awakes in a corresponding subframe, and blind-decodes a PDCCH by a PI-RNTI. If each of the UEs successfully performs blind decoding, each of the UEs determines that a paging message is present in the paging occasion selected by each UE and stores and decodes the paging message included in the PDSCH using the RB assignment information and the payload size of the PDCCH.
Each of the UEs can check that the paging message is transmitted to each UE, after decoding the PDSCH. If the paging message is checked, each of the UEs performs a random connection procedure and transitions to an active state. However, if the paging message is not transmitted to each UE, each UE transitions to a sleep mode again, awakes in a corresponding subframe again after the DRX cycle, and repeatedly performs the paging procedure.
Generally, the UEs which select the same paging occasion implicationally belong to the same group and the UEs belonging to the same group may be paged via one PDSCH. That is, if any one of the UEs belonging to the same paging group is paged, all the UEs belonging to the same paging group should decode a PDCCH and a PDSCH. Any one of the UEs within a cell have at least one group (e.g., within a paging occasion), implicitly.
Generally, if broadcasting information should be transmitted to all the UEs in the idle mode within a specific cell, the BS may use the paging procedure. For example, if the BS has broadcasting information which will be transmitted to all the UEs within the cell, the BS may transmit a paging message and the broadcasting information to the UEs via the PDSCH using a PI-RNTI in all paging occasions.
Unlike the paging message for transmitting different contents to the UEs belonging to each paging occasion (e.g., the UEs belonging to the same paging group), the broadcasting information transmits the same contents to all the UEs. The broadcasting information should be transmitted in all paging occasions regardless of whether or not the paging message has transmitted.
In FIG. 5, it is assumed that the broadcasting information is transmitted to the UE if the paging message is present in all the paging occasions and, in FIG. 6, it is assumed that the paging message is not present in all the paging occasions. As shown in FIGS. 5 and 6, the BS repeatedly transmits the same broadcasting information within all the paging occasions regardless of whether or not the paging message has transmitted. The broadcasting information is repeatedly transmitted within all the paging message periods regardless of whether or not the paging message has transmitted, and each of the UEs awakes in a predetermined paging subframe and decodes both the PDCCH and the PDSCH in order to receive the broadcasting information.
Generally, the BS transmits the broadcasting information to all the UEs using the PCH. That is, the broadcasting information is repeatedly transmitted by the number (n) of paging occasions in a paging message transmission period as shown in FIGS. 5 and 6.
Accordingly, since the BS repeatedly transmits the same broadcasting information to the UEs n times, overhead of a radio resource may be increased.
The generally used technology uses the same format as the PDCCH used when the DL scheduling grant is transmitted to the UEs in the active state via the PICH which is the control channel for paging.
Accordingly, the PICH may include information unnecessary for the transmission of the multicast and/or broadcasting information such as MIMO information, an MCS level and HARQ information as well as necessary information such as DL radio resource assignment information and the payload size. That is, since the BS continuously transmits unnecessary information via the PICH, a significant amount of radio resources may be wasted.
In the generally used technology, in order to allow the UE to receive the SI via the DBCH, the configuration of the physical HARQ indication channel (PHICH) is preferentially requested. Accordingly, it is preferable that the PHICH configuration information is transmitted via the MIB.
In the general technology, if the UE receives information transmitted via the PBCH once, the update is no longer requested. The PHICH configuration information may be changed. If the PHICH configuration information is changed, all the UEs can request the update of the information transmitted via the PBCH.
However, in the general technology, a method of updating the SI transmitted via the DBCH is defined, but a method of changing information about the PBCH is not defined. Accordingly, since the PHICH configuration information is transmitted to the UE via the PBCH, the method of updating the SI via the PBCH is necessary.